For FreeSpirit:
(someone sent this to me a while ago in an email; I'm just copying and pasting)
Valve Adjustment
This is meant as a walkthrough for us shade tree mechanics who don't really know what we're doing. As a DISCLAIMER, though, I must say that you take any responsibility for mistakes you make following this guide, even if the guide is wrong in some way. I am not a professional mechanic or even particularly experienced wrencher. First time I adjusted my valves, I did them 180 degrees out of phase (i.e. the engine was at TDC on the exhaust stroke). Got it right on the next try.
Understanding what you are going to do
We have an one overhead camshaft, with two lobes, one for intake and one for exhaust. The lobes push on the rockers. Each rocker has two rocker arms, which means we have four valves. The end of each rocker arm is threaded to accept a screw. As the cam turns, it pushes the rocker arms up and down. The screws push on the end of the valve stems. The screws are secured with nuts above the rocker arms. I call these nuts "locking nuts."
In the following diagram, the rocker arms are the bird foot looking things, more or less labeled "10" and "7." The valve stems are labeled "31" and "30." The adjustment screws are "11" and "8," and the locking nuts are "12" and "9." It is between the end of the adjustment screw and valve stem that you will be measuring the clearance.
picture:
Remove both valve inspection covers with a 10 mm wrench. Put the covers somewhere clean and safe. I strongly recommend throwing away these bolts and replacing them with new ones. the stock ones are very soft and easy to snap. See pics. They are M6 with a 1.0 pitch. Your local hardware store should have them. Just take one in and match it.
Now we must set the cam position properly. This is probably the trickiest or second trickiest part.
Put the bike in neutral.
As Dan recommends, stuff the long CLEAN Philips head screw driver in the spark plug hole. While doing the rest of this be careful not to let the screw driver bind against the side of the spark plug hole as the piston comes up.
The trick here is to find Top Dead Center (TDC) on the compression stroke. This is a 4-stroke engine, so the piston goes up and down twice, and the flywheel turns 2 whole rotations (720 degrees) for every 1 time the cam goes around.
Take the 17 mm offset wrench and turn the flywheel COUNTER CLOCKWISE WHILE LOOKING AT THE LEFT HAND SIDE OF THE BIKE. The Clymer manual has this wrong! It says to go clock wise! NO! You want to turn the flywheel in the same direction the wheels turn while going forward.
Turn the flywheel around several times while watching the rocker arms and the screw driver go up and down to get a feel for what's going on. You will be at TDC on the compression stroke when:
both sets of rocker arms should be up (edited from: "both rocker arms are down" ...), the lobes on the cam will be down, but you can't see this
the piston is at max height, or as Dan says, the piston just starts to go back down. Use the screw driver in the spark plug hole to determine this.
There should be a little play in the rocker arms now.
Check that the timing marks on the flywheel and the crank case more or less line up.
Don't be afraid to keep turning the flywheel counter clockwise until you get the hang of it and are confident that you are at TDC on the COMPRESSION STROKE.
NOTE: Now is the time to adjust the decompression cable free play as discussed above. If you do not have a 17mm offset wrench or are too cheap to buy one, there are 2 other methods:
You can use a 17 mm deepwall socket w/ a 3/8" drive, but this is tricky. Due to inertia, the ratchet tends to let the flywheel spin past where you want it to be. That's the way ratchets work; they are free to spin in one direction.
Put the bike in 5th (4th on pre , uh '95? models) gear and push it forward... while watching the rocker arms and screw driver. Or jack up the rear wheel and spin it so that the wheel turns in the forward direction.
Just go buy a 17 mm offset wrench.
Now we can actually measure the valve clearance and adjust it if necessary.
Clearance Measurement Procedure
Take your feeler gauge out. The specs call for a clearance of 0.003" to 0.005", NOT mm, for both intake and exhaust. In mm, it's 0.08 mm to 0.13 mm. On my feeler gauge, the top number is in inches, and the bottom is in mm. Only the bottom number is labeled. If you are not sure which is which, inches are bigger than mm. An exact conversion is: 1 inch = 25.4 mm.
Make sure the gauges are clean and free of dirt. Oil is okay (they should come oily). Also, the " notation 0.005" means inches and is very common.
Put the smallest gauge between the bottom of the adjustment screw (e.g. part number "11") and the end of the valve stem (e.g. part number "31"). If it fits, that's okay. Keep moving up in sizes until they won't fit. See a) through c) for the various cases. As for actually getting the gauges between the adjustment screw and the valve stem, it can be tricky. What I recommend: 1st, make sure there is plenty of light. If you are on the left side of the bike, measure the clearance on the right side while holding the rocker arm up with your other hand (remember there should be little play). Even if the gauge will fit, it may be tricky to get it in there. Practice sliding it in and out until you are sure you are measuring the right thing! I had the most success pushing the gauge straight in, but you can get them in from the side.
If the 0.005" fits, but not the 0.006", the clearance is to spec. Go to step 6) of "ADJUSTING THE CLEARANCE." However, you may want to tighten them up just a little. Your call.
If the 0.003" won't fit, your valves are too tight. Go to "ADJUSTING THE CLEARANCE."
If the 0.005" fits, try the next size up. If the next size up and so forth fits, the clearance is too loose. Go to "ADJUSTING THE CLEARANCE."
Adjusting The Clearance
If your valve stem - rocker arm adjustment screw clearance is out of spec, it's time to adjust the clearance.
Now the 10 mm offset wrench comes in very handy. You can also use a 10 mm socket w/ a wratchet (1/4" drive is easiest), but you can't hold the screw in place while you tighten the locking nut later w/ the wratchet. You may be able to get a regular 10 mm wrench in there, but not easily and you may mess up the nuts.
Loosen the locking nut(s) with the 10 mm offset wrench. This means turning the nut counter clockwise as you look down on it. This will bring the nuts "up," towards where the gas tank would normally be. If you are still not sure, point the thumb on your RIGHT HAND up, and your fingers will point in the direction you should turn the wrench.
Don't go crazy, sure and steady doesn't strip the nut or bend the adjustment screw. I DO NOT RECOMEND REMVOING THE NUTS. If they fall into the engine... well, God help you.
With a flat head screw driver, loosen (same direction as immediately above) the adjustment screw.